Pressures sensitive recording materials of the kind which utilize the coloration reaction of a color former (which can form a color by donating an electron or by accepting a proton from an acid or the like) with a color developer (which is a substance capable of accepting an electron or donating a proton, e.g., clay substances such as acid clay, activated caly, attapulgite, zeolite, bentonite and kaoline, organic acids such as salicylic acid, tannic acid, gallic acid and phenolic compounds, metal salts of these acids, and acidic polymers like phenol-formaldehyde resin) have so far been well-known. Such recording materials are described, e.g., in U.S. Pat. Nos. 2,505,470, 2,505,489, 2,550,471, 2,548,366, 2,712,507, 2,730,456, 2,730,457 and 3,418,250, Japanese Patent Application (OPI) Nos. 28411/74 (corresponding to U.S. Pat. No. 3,896,255) and 44009/75 (the term "OPI" as used herein means an "published unexamined Japanese patent application"), and so on.
A color former layer of pressure sensitive copying paper is obtained by dissolving a color former in a solvent, dispersing the resulting solution into a binder or enmicrocapsulating the solution, and then coating it on a support such as paper, plastic films, resin-coated paper and the like.
On the other hand, a color developer sheet is obtained by dissolving or dispersing a color developer together with a binder in a medium, such as water or the like, and coating it on a support.
In general, a color former and a color developer are coated on the same side of a support, on the front and the back sides of a support respectively, or on separate supports.
When pressure is applied to copying paper with a pen or a typewriter, a color former enclosed in microcapsules is released in the pressure-applied positions. The released color former then comes into contact with a color developer. Thereupon, color development takes place, and a record corresponding to applied pressures is obtained.
As described above, various kinds of substances are known as a color developer usable in a pressure sensitive recording material.
However, colors produced by using clays, such as activated clay, acid clay, etc., which have been prevailingly employed as a color developer up to the present, suffer from such defects as poor light or water resistance, poor stability with the elapse of time, and so on.
As for the color developers free from the above-described defects, organic color developers are known.
In general, a color developer sheet is produced as follows. A coating composition (A) is prepared by mechanically dispersing an organic color developer into water together with an inorganic pigment, a binder, a dispersant and other additives. Alternatively, a coating composition (B) is prepared by dissolving an organic color developer in an organic solvent, emulsifying the solution in water and adding an inorganic pigment, a binder and other additives to the emulsion. Next, (A), (B) or a mixture of (A) and (B) is coated on a support to produce a actual color developer sheet.
Although the color developer sheets obtained in these manners have various excellent properties, they still exhibit insufficinet fastness to light.